They are parents now, they conceded, but they are also children of the sixties who know the value of a good demonstration. That is why the parents of youngsters attending Harmony Hills Elementary School in Silver Spring decided to stage a sit-in demonstration in front of the school over the weekend to protest its closing.

About 250 parents, ranging in age from late 20s to early 40s, began the sit-in vigil at 7:30 p.m. Friday. The vigil will end tonight at 7:30 in the school gym.

The protest would not have been necessary, some parents said, if school board members had listened to their pleas when they used the traditional methods of attention getting - telephoning officials, writing letters of protest, holding meetings to make their views known.

"We tried all the other options open to us. We did it sanely and we went by all the guidelines. But we felt that our points weren't being made," said Sally Farrokhshahab.

"We're not radicals,' said Jane Sheldon, another parent. "But we felt our backs were up against the wall . . . our calls and letters to the school board weren't enough."

On the surface yesterday, the demontsration looked more like a neighborhood outing. The parents brought along lawn chairs for their "sit-in," along with a coffee urn, pitchers of soft drinks and boxes of cookies. Some even parked campers in front of the school.

Their children, meanwhile, occupied themselves during the day by playing games and riding bikes and tricycles around their protesting parents.

Around the school, the parents had planted signs which read, "Harmony Hills Is A Jewel of a School," "Let All Montgomery Schools Have a Fair Shake" and "It could Happen To You."

"I really feel this (protest) has brought the community closer," said one parent who had been present all night Saturday.

The Harmony Hills parents have asked the school board to grant an appeals hearing over the closing.Board member Blair Ewing, however, said it is unlikely the board will grant the hearing when it votes on the matter tomorrow, or that it will change its mind the 4-to-2 vote about closing Harmony Hills. Ewing and Marian Greenblatt cast the only opposition votes.

Harmony Hills is one of six schools the board voted to close this year because of declining enrollments. Other elementary schools slated for closing are Aspen Hill, Tuckerman, Maryvale, Holiday Park and Woodley Gardens.